/**
 * Copyright 2006 The Apache Software Foundation
 * <p>
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * <p>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.hadoop.examples;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.TreeMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;

public class ExampleDriver {

    /**
     * A description of an example program based on its class and a
     * human-readable description.
     *
     * @author Owen O'Malley
     * @date feb 2006
     */
    static private class ProgramDescription {

        static final Class[] paramTypes = new Class[]{String[].class};

        /**
         * Create a description of an example program.
         *
         * @param mainClass   the class with the main for the example program
         * @param description a string to display to the user in help messages
         * @throws SecurityException     if we can't use reflection
         * @throws NoSuchMethodException if the class doesn't have a main method
         */
        public ProgramDescription(Class mainClass,
                                  String description) throws SecurityException, NoSuchMethodException {
            this.main = mainClass.getMethod("main", paramTypes);
            this.description = description;
        }

        /**
         * Invoke the example application with the given arguments
         *
         * @param args the arguments for the application
         * @throws Throwable The exception thrown by the invoked method
         */
        public void invoke(String[] args)
                throws Throwable {
            try {
                main.invoke(null, new Object[]{args});
            } catch (InvocationTargetException except) {
                throw except.getCause();
            }
        }

        public String getDescription() {
            return description;
        }

        private final Method main;
        private final String description;
    }

    private static void printUsage(Map programs) {
        System.out.println("Valid program names are:");
        for (Object o : programs.entrySet()) {
            Entry item = (Entry) o;
            System.out.println("  " + item.getKey() + ": " +
                    ((ProgramDescription) item.getValue()).getDescription());
        }
    }

    /**
     * This is a driver for the example programs.
     * It looks at the first command line argument and tries to find an
     * example program with that name.
     * If it is found, it calls the main method in that class with the rest
     * of the command line arguments.
     *
     * @param args The argument from the user. args[0] is the command to run.
     * @throws NoSuchMethodException
     * @throws SecurityException
     * @throws IllegalAccessException
     * @throws IllegalArgumentException
     * @throws Throwable                Anything thrown by the example program's main
     */
    public static void main(String[] args)
            throws Throwable {
        Map programs = new TreeMap();

        // Add new programs to this list
        programs.put("wordcount", new ProgramDescription(WordCount.class,
                "A map/reduce program that counts the words in the input files."));
        programs.put("grep", new ProgramDescription(Grep.class,
                "A map/reduce program that counts the matches of a regex in the input."));

        // Make sure they gave us a program name.
        if (args.length == 0) {
            System.out.println("An example program must be given as the" +
                    " first argument.");
            printUsage(programs);
            return;
        }

        // And that it is good.
        ProgramDescription pgm = (ProgramDescription) programs.get(args[0]);
        if (pgm == null) {
            System.out.println("Unknown program '" + args[0] + "' chosen.");
            printUsage(programs);
            return;
        }

        // Remove the leading argument and call main
        String[] new_args = new String[args.length - 1];
        System.arraycopy(args, 1, new_args, 0, args.length - 1);
        pgm.invoke(new_args);
    }

}
